I've been staring at debug output for hours this evening (yes, I know its Friday night [headshake]) and its not making any more sense.
I seemed to get a good lead on texel addressing though. They moved the texel 'centre' with D3D10, but I thought that should really match up fine with my CPU-generated look-up texture.
Then I hit on some obscure fringe cases where it was wrapping around and pulling in completely incorrect values. Clamping appears to have eliminated those, but the overall result is still not sufficiently good for my liking.
My first task tomorrow is going to be to rewrite my look-up texture code to use render-to-texture instead. I can easily rewrite my shader(s) so that the exact same code is used in the non-lookup versus the lookup paths, and if that still generates different results then I think I might actually scream [smile]